Fabrication of pressureless sintered dense β-SiAlON via a reaction-bonding route with ZrO 2 addition

Abstract

A reaction-bonding and post-sintering process was applied to fabricate pressureless sintered β-Si 6− Z Al Z O Z N 8− Z ( Z = 1–3) ceramics with monoclinic ZrO 2 added to the starting powder. Samples with ZrO 2 showed enhanced nitridation and achieved near theoretical density following post-sintering, although this could not be achieved in the samples produced without ZrO 2. Thus the ZrO 2 is effective in both enhancing the nitridation of Si and as a sintering additive for densification of β-SiAlON. Part of the added monoclinic ZrO 2 was transformed to tetragonal ZrO 2, and the ZrN phase was also formed due to reaction with nitrogen during the reaction-bonding process. After the post-sintering process, the ZrN phase remained only in the Z = 3 composition. In the other compositions the ZrN reacted with SiO 2 to form both tetragonal and monoclinic ZrO 2 phases. These differences are explained in terms of the increasing densification and grain growth for Al 2O 3 rich compositions and the ZrN being trapped inside such grains in the case of the Z = 3 sample.